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“Because jawless vertebrates are the most primitive vertebrates, they have been studied to MG-132 manufacturer gain understanding of the evolutionary processes that gave rise to the innate and adaptive immune systems in vertebrates. Jawless vertebrates have developed lymphocyte-like cells that morphologically resemble the T and B cells of jawed vertebrates, but they express variable lymphocyte receptors (VLRs) instead of the T and B cell receptors that specifically recognize antigens in jawed vertebrates. These VLRs act as antigen receptors,

diversity being generated in their antigen-binding sites by assembly of highly diverse leucine-rich repeat modules. Therefore, jawless vertebrates have developed adaptive immune systems based on the VLRs. Although pattern recognition receptors, including Toll-like receptors (TLRs) and Rig-like receptors (RLRs), and their adaptor genes are conserved in jawless vertebrates, some transcription factor and inflammatory cytokine

genes p38 MAPK pathway in the TLR and RLR pathways are not present. However, like jawed vertebrates, the initiation of adaptive immune responses in jawless vertebrates appears to require prior activation of the innate immune system. These observations imply that the innate immune systems of jawless vertebrates have a unique molecular basis that is distinct from that of jawed vertebrates. Altogether, although the molecular details of the innate and adaptive immune systems differ between jawless and jawed vertebrates, jawless vertebrates have developed versions of these immune systems that are similar to those of jawed vertebrates. Vertebrate immune systems have innate and adaptive immunity components. In these immune

systems, different types of receptors play important roles in pathogen recognition. Innate immunity provides the first line of defense against pathogens. In the innate immune system, PRRs, such as the TLRs, NLRs and RLRs, recognize PAMPs [1]. Recognition of PAMPs rapidly induces antimicrobial responses in infected cells and activates innate immune cells, including macrophages and DCs, that act as APCs[2]. In contrast, antigen-specific Dichloromethane dehalogenase responses and immunological memory characterize the adaptive immunity system. In this immune system, TCRs and BCRs act as antigen-specific receptors on T and B cells, respectively. An assembly of variable (V) and joining (J), or V, diversity (D) and J gene fragments generate variability in the antigen-binding regions of these receptors [3]. RAGs mediate rearrangement of the antigen receptor genes. The antigen receptors allow the organisms to have an immune repertoire that is able to specifically recognize virtually any antigen. Whereas BCRs and their soluble form, antibodies, directly recognize antigens, TCRs recognize processed antigen peptide and MHC molecule complexes on infected cells and APCs [4].